The invention relates to a centralized command system for a telecommunications network, in which system a central exchange of a telecommunications network and network elements, such as local concentrators, under its control form an entity which is controllable in a centralized manner from the central exchange by means of user interfaces of individual concentrators.
It is becoming more and more general to use concentrators of different levels in connection with digital exchanges in public telecommunications networks. By the use of concentrators, subscribers can be effectively gathered from a wide area to a large tandem or regional exchange. Concentrators are placed in villages and, as the capacity increases, presently even in small towns.
A central exchange with its concentrators can thus offer digital telephone services over a wide area. From the point of view of an operator, such a concept has several advantages. Subscribers can be numbered freely on the entire wide exchange area. The operation of the exchange is centralized, and the whole large entity can be treated as one exchange. All management tasks, such as the control of subscribers, or the updating and changing of software, can be effected in a centralized manner.
The central exchange and its concentrators are operated in a centralized manner from the central exchange. On the other hand, the concentrators are required to operate very independently, particularly when connections to the central exchange are broken. A concentrator must be capable of switching internal traffic without the control of the central exchange, and it must be possible to store the computed data produced by it during the break.
There are two alternative ways of implementing concentrators. A concentrator can be developed from an independent exchange or from a simpler subscriber level. When it is developed from an independent exchange, a large number of features of independent operation can easily be included in it. The problem is rather how to arrange uniform operation functions in such a manner that a plurality of entities "independent" from an operational point of view are seen by the user as in a single large exchange.
In practice, this often means that the operation and control tasks pertaining to the entire network are divided into several subtasks to be carried out in different parts of the network (i.e. in concentrators). The management of the whole task requires strict control of the subtasks and an ability to cope with many fault situations, which may occur when only part of the tasks can be carried out in a controlled manner.